1. Field
The present invention generally relates to a microchip for electrophoresis, and more particularly to a glass microchip, which has an optical slit made from silicon by MEMS fabrication to effectively cut off a stray light. Further, the present invention relates to a method of manufacturing the same.
2. Background
A micro total analysis system (μTAS), which was established along with advancements of nano and bio technologies, became an essential foundation for a bioMEMS technology. An electrophoretic analysis is mainly used in the μTAS. With regard to selecting channels in which a sample is separated, the electrophoretic analysis is recently being changed from one way of using a fused silica capillary to another way of using a lab-on-a-chip, which is manufactured by MEMS fabrication and micromachining technology. Such electrophoretic analysis using a microchip is attracting great attention as an emergent analysis technology. This is due to the treatment of a small amount of samples, a faster analysis, more convenient operation, a high throughput with improved accuracy, etc.
Various samples such as proteins, DNAs, amino acids, cell particles, etc. can be analyzed by using the electrophoresis microchip. The electrophoresis microchip basically utilizes a microfluidics principle. The electrophoresis microchip is provided with a sample loading channel (into and out of which sample solution to be analyzed flows) and a separation channel (into and out of which buffer solution flows), and which is crossed to the sample loading channel. Inlet and outlet reservoirs of the sample solution and the buffer solution are provided with electrodes so that electric fields can be applied to the sample loading channel and the separation channel. While the sample solution flows from the inlet reservoir to the outlet reservoir, a certain amount of sample solution is positioned at an intersection of the sample loading channel and the separation channel by the electric field applied to the sample loading channel. Then, particles dispersed in the sample solution are separated according to the mobility differences by the electric field applied to the separation channel. The dimensions of the channel of the microchip are several tens μm to about 100 μm in width and depth.
Plastics such as polydimethylsiloxane (PDMS), quartz, glass, silicon, etc. are used as a material for the microchip. The microchip made from PDMS is used as a disposable chip and the manufacturing costs are low. On the contrary, the microchips made from quartz, glass, silicon, etc. are possible to be used repeatedly since they are manufactured by dry and wet etching and bonding, which require high process costs.
In case the microchip is made from quartz or glass, a UV detector can be introduced in order to analyze the samples. FIG. 1 depicts an electrophoresis system equipped with the UV detector introduced thereto. The UV detector has relatively low costs and can be conveniently operated compared to any other detector such as a fluorescence detector. In addition, since signals are received from the entire channel region by means of zone detection, transports of the samples to be analyzed in the channel can be observed in real time. In such an electrophoresis system with the UV detector, in order to enhance a peak intensity (i.e., a signal-to-noise ratio (S/N ratio) of UV light), a technology for manufacturing a microchip, which allows the incident UV light to focus on only the channel and the stray light to cut off except the channel region, is necessary.
As a current technical state relevant to such a technology, the following papers disclose microchips, wherein an optical slit made of Si/SiO2 is provided between the channel plate and the reservoir plate: a paper entitled “Single-step quantitation of DNA in microchip electrophoresis with linear imaging UV detection and fluorescence detection through comigration with a digest” (F. Xu et al.) published in the Journal of Chromatography A, vol. 1051, pp. 147-153, 2004; a paper entitled “High-speed electrophoretic analysis of 1-phenyl-3-methyl-5-pyrazolone derivatives of monosaccharides on a quartz microchip with whole-channel UV detection” (S. Suzuki et al.) published in the Electrophoresis, vol. 24, pp. 3828-3833, 2003; a paper entitled “Fabrication of quartz microchip with optical slit and development of a linear imaging UV detector for microchip electrophoresis systems” (H. Nakanishi et al.) published in the Electrophoresis, vol. 22, pp. 230-234, 2001; a paper entitled “Studies on SiO2—SiO2 bonding with hydrofluoric acid. Room temperature and low stress bonding technique for MEMS” (H. Nakanishi et al.) published in the Sensors and Actuators, vol. 79, pp. 237-244, 2000. Those microchips have been developed to be limited to only quartz material and are being marketed by Shimadzu Instruments (Kyoto, Japan).
However, quartz material is expensive. In addition, both dry etching and wet etching are required in order to form the channels on the channel plate made from quartz. Therefore, there is a problem with the microchip made from quartz in that its material is expensive and its process and manufacturing costs are high. Because wet etching is apt to render the cross-sectional shape of the channel isotropic while causing undercuts in the channel, the channel of the microchip formed by wet etching is further or less etched than the desired depth and width. There is another problem with the microchip made from quartz in that it is difficult to bond the channel plate and the reservoir plate during manufacturing the microchip.
Accordingly, there is a need to provide an electrophoresis microchip made from a more inexpensive material than quartz (e.g., glass) to reduce operation costs and to facilitate microchip supply. Further, there is a need to provide an electrophoresis microchip, wherein its channels are formed by dry etching instead of wet etching in order to render the cross-sectional shape of the channel anisotropic and to reduce process costs. Furthermore, there is a need to provide an electrophoresis microchip, which is configured such that a channel plate and a reservoir plate are easily bonded.